Light-emitting metal-oxide-semiconductor devices and associated systems, devices, and methods

ABSTRACT

Various embodiments of solid state transducer (“SST”) devices are disclosed. In several embodiments, a light emitter device includes a metal-oxide-semiconductor (MOS) capacitor, an active region operably coupled to the MOS capacitor, and a bulk semiconductor material operably coupled to the active region. The active region can include at least one quantum well configured to store first charge carriers under a first bias. The bulk semiconductor material is arranged to provide second charge carriers to the active region under the second bias such that the active region emits UV light.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. patent application Ser. No.16/536,528, filed Aug. 9, 2019; which is a continuation of U.S. patentapplication Ser. No. 15/976,794, filed May 10, 2018, now U.S. Pat. No.10,418,509; which is a continuation of U.S. patent application Ser. No.15/249,140, filed Aug. 26, 2016, now U.S. Pat. No. 9,997,662; which is adivisional of U.S. patent application Ser. No. 13/918,655, filed Jun.14, 2013, now U.S. Pat. No. 9,433,040; each of which are incorporatedherein by reference.

TECHNICAL FIELD

The present disclosure is related to electrical contacts in lightemitting semiconductor devices, such as light emitting diodes (“LEDs”)and other solid state transducer (“SST”) devices.

BACKGROUND

SST devices can have light emitting dies with different electrodeconfigurations. For example, FIG. 1 is a cross-sectional view of a lightemitting device 100. As shown, the light emitting device 100 includes asubstrate 101 carrying an LED structure 102 comprised of N-type galliumnitride (GaN) 104, one or more GaN/indium gallium nitride (InGaN)quantum wells (QWs) 105, and P-type GaN 106. The light emitting device100 also includes a first electrode 108 on the N-type GaN 104 and asecond electrode 109 on the P-type GaN 106. In operation, a voltageapplied across the electrodes generates electron/hole pairs in theactive regions of the LED structure 102. When these pairs recombine,energy is released, including energy in the form of emitted light. Ingeneral, the wavelength of the emitted light is based on the energydifference between the electrons and holes before they recombine.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a light emitting deviceconfigured in accordance with the prior art.

FIG. 2 is a schematic cross-sectional diagram of an SST system having alight emitter and a waveform generator configured in accordance with anembodiment of the present technology.

FIGS. 3A and 3B are a schematic cross-sectional diagram and an energyband diagram of the light emitter of FIG. 2 at equilibrium in accordancewith an embodiment of the present technology.

FIGS. 4A and 4B are a schematic cross-sectional diagram and an energyband diagram of the light emitter of FIG. 2 under reverse bias inaccordance with an embodiment of the present technology.

FIGS. 5A and 5B are a schematic cross-sectional diagram and an energyband diagram of the light emitter of FIG. 2 under forward bias inaccordance with an embodiment of the present technology.

FIG. 6 is a flow diagram illustrating a method for operating the lightemitter of FIG. 2 in accordance with an embodiment of the presenttechnology.

FIGS. 7A-7C show accumulated charge, discharge current, and photon flux,over a high frequency charge/discharge cycle of the light emitter ofFIG. 2 in accordance with an embodiment of the present technology.

FIGS. 8A-8C show charge accumulation, current discharge, and photonflux, over a low frequency charge/discharge cycle of the light emitterof FIG. 2 in accordance with an embodiment of the present technology.

FIG. 9 is a signal line diagram showing a bias signal configured to havea duty cycle for operating the light emitter of FIG. 2 in accordancewith an embodiment of the present technology.

FIG. 10 is a schematic view of a system that includes a light emitterconfigured in accordance with selected embodiments of the presenttechnology.

DETAILED DESCRIPTION

Various embodiments of light emitting devices, SST systems with lightemitters, and associated methods are described below. As usedhereinafter, the term “light emitter” generally refers to devices withone or more solid state light emitting devices, dies, and/or substrates,such as LEDs, laser diodes (“LDs”), and/or other suitable sources ofillumination other than electrical filaments, a plasma, or a gas. Aperson skilled in the relevant art will also understand that thetechnology may have additional embodiments, and that the technology maybe practiced without several of the details of the embodiments describedbelow with reference to FIGS. 2-10 .

Conventional ultraviolet (UV) light emitters typically employarrangements of GaN and aluminum GaN (AlGaN) materials. The AlGaNmaterials, in particular, can have alloyed/engineered concentrations ofaluminum, N-type dopant, and P-type dopant to achieve a certain UVwavelength and/or spectrum of wavelengths. In operation, N-type andP-type AlGaN at least partially define a quantum well, with the P-typeAlGaN configured to inject P-type charge carriers (i.e., holes) into thequantum well. One problem, however, with P-type AlGaN is that it has lowconductivity and low light extraction efficiency. The conductivity islow because the acceptor species (e.g., magnesium (Mg)) has a highactivation energy. The light extraction efficiency is low because P-typeAlGaN is not compatible with the highly reflective materials ordinarilyavailable for Ohmic connections in (non-UV) light emitters. As a result,conventional UV light emitters can have operational efficiencies thatare less than 5%. Embodiments of the present technology, however,address these and other limitations of conventional UV light emittersand other conventional emitters.

FIG. 2 is a schematic cross-sectional diagram of an SST system 200having a light emitter 210 and a waveform generator 230 configured inaccordance with an embodiment of the present technology. The lightemitter 210 includes a semiconductor structure 212, a first electrode213, and a second electrode 215. The semiconductor structure 212includes a bulk semiconductor material 216 (“bulk material 216”), anoptional spacer 217, and an active region 218 between the bulk material216 and the spacer 217. The bulk material 216 can include, for example,a single grain semiconductor material (e.g., N-type AlGaN) with athickness greater than about 10 nanometers and up to about 500nanometers. The spacer 217 can include, for example, a single grainsemiconductor material (e.g., GaN or AlGaN). The active region 218 caninclude a single quantum well (“SQW”) or multiple quantum wells “MQWs.”In one embodiment, the active region 218 includes a single grainsemiconductor material (e.g., GaN or AlGaN) with a thickness in therange of about 1 nanometer to 10 nanometers. In another embodiment, theactive region 218 includes a semiconductor stack of such materials.

The first electrode 213 includes a first conductive contact 219 aconnected to the bulk material 216. The second electrode 215 includes asecond conductive contact 219 b and a dielectric material 220 betweenthe second conductive contact 219 b and the spacer 217. The conductivecontacts 219 can include, for example, a metal, a metal alloy, a dopedsilicon, and/or other electrically conductive substrate materials. Thedielectric material 220 can include, for example, silicon oxide (SiO₂),silicon nitride (Si₃N₄), and/or other suitable non-conductive materialsformed on the semiconductor structure 212 via thermal oxidation,chemical vapor deposition (“CVD”), atomic layer deposition (“ALD”),and/or other suitable techniques. In other embodiments, the dielectricmaterial 220 can include a polymer (e.g., polytetrafluoroethylene and/orother fluoropolymer of tetrafluoroethylene), an epoxy, and/or otherpolymeric materials.

The waveform generator 230 is configured to output a bias signal. In theillustrated embodiments, the waveform generator 230 produces a squarewave having a first voltage V₁ and a second voltage V₂. In otherembodiments, however, the waveform generator 230 can output other typesof waveforms having various pulse shapes, frequencies, voltages,current, power, etc. Because the basic structures and functions ofwaveform generators are known, they have not been shown or described infurther detail to avoid unnecessarily obscuring the describedembodiments.

In operation, the light emitter 210 functions similar to a capacitor(e.g., a metal-oxide-semiconductor (MOS) capacitor). The waveformgenerator 230 applies the first voltages V₁ to reverse bias the lightemitter 210, and it applies the second voltage V₂ to forward bias thelight emitter 210. As described in greater detail below, the reversebias stores charge in the light emitter 210 and the forward biasreleases the charge to emit light. In one embodiment, the light emitter210 emits UV light (having wavelengths, e.g., in the range of 10 nm to400 nm). In another embodiment, the light emitter 210 employs AlGaNmaterials, but not P-type AlGaN materials, to produce the UV light. Assuch, the light emitter 210 can have a larger conductivity and higherlight extraction efficiency than conventional UV light emitters.

For purposes of clarity, only certain components of the SST system 200have been shown in the illustrated embodiments. However, SST systemsconfigured in accordance with various embodiments of the presenttechnology can include other components. For example, in someembodiments the SST system 200 can include a lens, a mirror, and/orother suitable optical and/or electrical components.

FIGS. 3A and 3B are a schematic cross-sectional diagram and an energyband diagram of the light emitter 210 at equilibrium. Referring to FIGS.3A and 3B together, the second conductive contact 219 b has a firstFermi level E_(F1). The semiconductor structure 212 includes a valenceband E_(v), a conduction band E_(c), and a second Fermi level E_(F2)that is aligned with the first Fermi level E_(F1). The semiconductorstructure 212 also includes a quantum well 323 having available chargecarrier (i.e., hole) energy states above the valence band E_(v) andavailable charge carrier (i.e., electron) energy states below theconduction band E_(c). As shown, the valence and conduction bands E_(v)and E_(c) bend upwards at the left-hand side of the quantum well 323,but they are generally flat within the region of the spacer 217. In someembodiments, the spacer 217 can include an intrinsic or lightly N-typedoped material to reduce or eliminate interfacial states (i.e., defectstates) between the quantum well 323 and the dielectric material 220. Assuch, the spacer 217 can directly contact the active region 218 (i.e.,without a semiconductor material between the spacer 217 and the activeregion 218). In other embodiments, however, the spacer 217 can be absentfrom the light emitter 210.

FIGS. 4A and 4B are a schematic cross-sectional diagram and an energyband diagram of the light emitter 210 under reverse bias. Referring toFIGS. 4A and 4B together, the first voltage V₁ raises the first Fermilevel E_(F1) above the second Fermi level E_(F2) to bring the activeregion 218 into inversion. As shown, the first voltage V₁ produces afirst electric field E₁ across the dielectric material 220 that depleteselectrons from the active region 218. The electric field E₁ also drawsholes 425 from the bulk material 216 into the active region 218. Thequantum well 323 traps the holes 425 and accumulates an electricalcharge Q₁ (“accumulated charge Q₁”). In general, the accumulated chargeQ₁ can be based on factors such as the magnitude of the first voltageV₁, a pulse width of the first voltage V₁, the number of quantum wellsat the active region 218, the resistivity of the semiconductor structure212, etc. As described in greater detail below, under a reverse bias,the accumulated charge Q₁ increases as a function of time to a maximumcharge level Q_(Max).

FIGS. 5A and 5B are a schematic cross-sectional diagram and an energyband diagram of the light emitter 210 under forward bias. Referring toFIGS. 5A and 5B together, the second voltage V₂ lowers the first Fermilevel E_(F1) below the second Fermi level E_(F2) to bring the activeregion into accumulation. The second voltage V₂ produces a secondelectric field E₂ in the dielectric material 220 that draws electrons527 from the bulk material 216 into the active region 218. When theelectrons 527 recombine with the holes 425 in the quantum well 323, theyemit light 528 (e.g., UV light). Also, the electrons 527 that flowthrough the bulk material 216 produce a discharge current i₁ thateventually depletes (e.g., partially or fully depletes) the accumulatedcharge Q₁. As described in greater detail below, under a forward bias,the accumulated charge Q₁ decreases as a function of time to a minimumcharge level Q_(Min).

FIG. 6 is a flow diagram illustrating a method 600 for operating thelight emitter 210 in accordance with an embodiment of the presenttechnology. In one aspect of the embodiment of FIG. 6 , the method 600is a carried out by the waveform generator 230 (FIG. 2 ). The method 600begins after a start block. For example, the method 600 can start afterpowering on the SST system 200. At block 641, the waveform generator 230charges the light emitter 210 in a “charge mode.” In this mode, thewaveform generator 230 can apply a first phase of a bias signal to thelight emitter 210. The first phase can include a first waveform thatreverse biases the active region 218 (FIG. 2 ). For example, a portionof the first waveform can have a signal level at the first voltage V₁.As described in greater detail below, the charge mode has an elapsedcharge time Δt_(C) (“charge time Δt_(C)”).

At block 642, the waveform generator 230 discharges the light emitter210 in a “discharge mode.” In this mode, the waveform generator 230 canapply a second phase of the bias signal to the light emitter 210. Thesecond phase can include a second waveform that forward biases theactive region 218. For example, a portion of the second waveform canhave a signal level at the second voltage V₂. As described in greaterdetail below, the discharge mode has an elapsed discharge time Δt_(D)(“discharge time Δt_(D)”).

At decision block 643, the waveform generator 230 completes acharge/discharge cycle, and it can return to block 641 to carry outanother charge/discharge cycle. In several embodiments, the frequency ofthe charge/discharge cycle can be based on the charge time Δt_(C) andthe discharge time Δt_(D), as shown by Equation 1.f ₁=1/(Δt _(C) +Δt _(D))  (1)

FIGS. 7A-7C show accumulated charge (FIG. 7A), discharge current (FIG.7B), and photon flux (FIG. 7C) over a high frequency f_(H)charge/discharge cycle of the light emitter 210 in accordance with anembodiment of the present technology. Without being bound by theory, itis believed that the charge and discharge modes function in a mannersomewhat analogous to a MOS capacitor. However, unlike a conventionalMOS capacitor, the discharge mode also emits electromagnetic radiation(e.g., UV light) from the capacitor.

FIG. 7A shows the accumulated charge Q₁ as a function of time over thehigh frequency f_(H) charge/discharge cycle. In charge mode, theaccumulated charge Q₁ (t) increases from the minimum charge levelQ_(Min) to the maximum charge level Q_(Max) over the charge time Δt_(C).In the discharge mode, the accumulated charge Q₁ (t) decreases from themaximum charge level Q_(Max) to the minimum charge level Q_(Min) overthe discharge time Δt_(D).

FIG. 7B shows the discharge current i₁(t) as a function of time over thehigh frequency f_(H) charge/discharge cycle. Without being bound bytheory, it is believed that the discharge current i₁(t) is proportionalto the recombination rate τ of electron in the active region 218 (FIG. 2). Also, because the cycle frequency is high, it is believed that in thecharge mode, the electrons in the active region do not completelydissipate. Accordingly, for small differences in the maximum and minimumaccumulated charge, the discharge current I₁ can be approximated, asshown by Equation 2.I_(AVG)˜τ(Q_(Max)+Q_(Min))/2  (2)

FIG. 7C shows photon flux Φ₁(t) of emitted light (e.g., the light 528 ofFIG. 5 ) as a function of time over the high frequency f_(H)charge/discharge cycle. Without being bound by theory, it is believedthat the average photon flux Φ₁ is proportional to the discharge currentI₁(t). Accordingly, based on Equation 2 the average photon flux Φ₁ canbe approximated, as shown by Equation 3.Φ_(AVG)∝τ(Q_(Max)+Q_(Min))/2  (3)

FIGS. 8A-8C show accumulated charge (FIG. 8A), discharge current (FIG.8B), and photon flux (FIG. 8C) over a low frequency f_(L)charge/discharge cycle of the light emitter 210 in accordance with anembodiment of the present technology. In one respect, FIGS. 8A-8C aredifferent from FIGS. 7A-7C in that Δt_(C) (f_(L))>Δt_(C) (f_(H)) andΔt_(D) (f_(L))>Δt_(D) (f_(H)).

FIG. 8A shows the accumulated charge Q₁ as a function of time over thelow frequency f_(L) charge/discharge cycle. In charge mode, theaccumulated charge Q₁ (t) increases from zero charge to the maximumcharge level Q_(Max) over the charge time Δt_(C). In the discharge mode,the accumulated charge Q₁ (t) decreases from the maximum charge levelQ_(Max) to zero charge over the discharge charge time Δt_(D). Withoutbeing bound by theory (and similar to high/low frequency behavior of aMOS capacitor), it is believed that the maximum accumulated charge atlow frequency Q_(Max) (f_(L)) is greater than the maximum accumulatedcharge at high frequency Q_(Max) (f_(H)).

FIG. 8B shows the discharge current i₁(t) as a function of time over thelow frequency f_(L) charge/discharge cycle. Without being bound bytheory, it is believed that because the cycle frequency f_(L) is lowfrequency, the electrons in the active region dissipate during chargemode. As such, the discharge current i₁(t) ceases to flow over themajority of the charge time Δt_(C). Similar to FIG. 7B, it is believedthat during the discharge mode, current i₁(t) is proportional to therecombination rate τ of electron in the active region 218 (FIG. 2 ).

FIG. 8C shows photon flux Φ₁(t) of emitted light (e.g., the light 528 ofFIG. 5 ) as a function of time over the low frequency f_(L)charge/discharge cycle. Without being bound by theory, it is believedthat the maximum photon flux at low frequency Φ_(MAX) (f_(L)) is greaterthan the maximum photon flux at high frequency Φ_(MAX) (f_(H)). Inparticular, it is believed that this is due to larger amount ofaccumulated charge at the low frequency charge mode (FIG. 8A). In someembodiments, it is believed that the low cycling frequency f_(L) canemit pulsed light. For example, during the charge mode, the dischargecurrent can reduce to zero, such that the light emitter 210 does notoutput photons for a portion of the charge time Δt_(C). Accordingly, byappropriate selection of the duty cycle, it is believed that emittedlight can be shaped to have variously pulses widths.

FIG. 9 is a signal line diagram showing a bias signal S₁ configured tohave a duty cycle for operating the light emitter 210 in accordance withan embodiment of the present technology. The charge mode of the biassignal S₁ has a charge-mode duty cycle that can be represented byEquation 4 and a discharge-mode duty cycle that can be represented byEquation 5.Duty Cycle (Charge mode)=Δt _(C)/(Δt _(C) +Δt _(D))  (4)Duty Cycle (Discharge mode)=Δt _(D)/(Δt _(C) +Δt _(D))  (5)

In the illustrated embodiments, the duty cycle of the charge anddischarge modes is 50%. In other embodiments, however, the duty cyclecan be configured differently. For example, if the recombination rate τlimits the rate of discharge, the duty cycle of the charge mode can bereduced (e.g., to 25%) to reduce the charge time. As such, the dutycycled of the discharge mode will increase (e.g., to 75%) to allow moretime for discharge. In one embodiment, the duty cycle can be selected toprovide pulsed light. In another embodiment, the duty cycle can beselected to provide non-pulsed light. In certain embodiments, the biassignal S₁ can be configured to have other features, such as leadingand/or falling edges that are sloped, a time-varying duty cycle,multiple voltage levels, sinusoidal waveforms, etc. For example, thebias signal S₁ can include a first phase to initially charge (e.g., rampup) the light emitter 210 and a second phase to operate the lightemitter 210 at steady state (i.e., a steady state of pulsed light ornon-pulsed light).

The light emitter 210 and/or the SST system 200 described above withreference to FIGS. 2-9 can be used to form SST devices, SST structures,and/or other semiconductor structures that are incorporated into any ofa myriad of larger and/or more complex devices or systems, arepresentative example of which is system 1050 shown schematically inFIG. 10 . The system 1050 can include one or more semiconductor/SSTdevices 1051, a driver 1052, a processor 1053, and/or other subsystemsor components 1054. The resulting system 1050 can perform any of a widevariety of functions, such as backlighting, general illumination, powergenerations, sensors, and/or other suitable functions. Accordingly,representative systems can include, without limitation, hand-helddevices (e.g., mobile phones, tablets, digital readers, and digitalaudio players), lasers, photovoltaic cells, remote controls, computers,and appliances. Components of the system 1050 may be housed in a singleunit or distributed over multiple, interconnected units (e.g., through acommunications network). The components of the system 1050 can alsoinclude local and/or remote memory storage devices, and any of a widevariety of computer readable media.

From the foregoing, it will be appreciated that specific embodiments ofthe disclosure have been described herein for purposes of illustration,but that various modifications may be made without deviating from thedisclosure. For example, in some embodiments, the maximum and/or minimumaccumulated charge can be configured based on material properties, inaddition to or in lieu of the cycle frequency and/or the bias level.These material properties can include, for example, conductivity,carrier mobility, carrier effective mass, impurity concentration, etc.Also, the various waveforms shown in the Figures can have differentslopes, magnitudes, shapes, etc. Similarly, the semiconductor devices,substrates, and other features can have shapes, sizes, and/or othercharacteristics different than those shown and described with referenceto the Figures. For example, the conductive contacts 219 of the lightemitter 210 can have different configurations (e.g., lateral or verticalconfigurations). In addition, certain aspects of the disclosuredescribed in the context of particular embodiments may be combined oreliminated in other embodiments. Further, while advantages associatedwith certain embodiments have been described in the context of thoseembodiments, other embodiments may also exhibit such advantages. Not allembodiments need necessarily exhibit such advantages to fall within thescope of the present disclosure. For example, in some embodiments, lightemitters can be configured to work with P-type materials. Accordingly,the disclosure and associated technology can encompass other embodimentsnot expressly shown or described herein.

We claim:
 1. A light emitter, comprising: a semiconductor structureincluding an active region and a bulk material having a first surfaceand a third surface opposite the first surface and connected to a fourthsurface of the active region, wherein the active region is configured toemit electromagnetic radiation, and wherein the bulk material isconfigured to supply charge carriers to the active region; a firstelectrode including a first conductive contact directly connected to thefirst surface of the bulk material; and a second electrode including adielectric layer and a second conductive contact connected to thedielectric layer, wherein the dielectric layer is adjacent to a secondsurface of the active region opposite the fourth surface such that thesecond conductive contact, the dielectric layer, and the semiconductorstructure collectively form a metal-oxide-semiconductor capacitor. 2.The light emitter of claim 1, wherein: the active region includes afirst semiconductor material having a first bandgap energy; the bulkmaterial includes a second semiconductor material having a secondbandgap energy that is greater than the first bandgap energy; and thedielectric layer includes a dielectric material having a third bandgapenergy that is greater than the second bandgap energy.
 3. The lightemitter of claim 1, wherein the active region includes one or morequantum wells.
 4. The light emitter of claim 1, wherein thesemiconductor structure includes AlGaN materials exclusive of p-typeAlGaN materials.
 5. The light emitter of claim 1, wherein the dielectriclayer is configured to support an electric field that draws the chargecarriers from the bulk material to the active region when a voltageapplied to the second electrode.
 6. The light emitter of claim 1,wherein the dielectric layer includes polymeric materials.
 7. The lightemitter of claim 1, wherein the active region is configured toaccumulate the charge carriers supplied from the bulk material inresponse to a reverse bias applied between the first conductive contactand the second conductive contact.
 8. The light emitter of claim 7,wherein the active region is configured to emit the electromagneticradiation while the charge carriers accumulated therein are depleted inresponse to a forward bias applied between the first conductive contactand the second conductive contact.
 9. The light emitter of claim 1,further comprising: a spacer disposed between the active region and thedielectric layer, the spacer including an intrinsic or lightly dopedsemiconductor material.
 10. The light emitter of claim 9, wherein theintrinsic or lightly doped semiconductor material includes a fourthbandgap energy that is greater than a first bandgap energy of a firstsemiconductor material that the active region includes.
 11. A method ofoperating a light emitter, comprising: applying a first voltage to anelectrode of the light emitter, the electrode including a dielectriclayer adjacent to an active region of a semiconductor structure of thelight emitter, wherein the first voltage is configured to bring theactive region into inversion; and applying a second voltage to theelectrode after applying the first voltage, wherein the second voltageis configured to bring the active region into accumulation, therebyemitting electromagnetic radiation from the active region.
 12. Themethod of claim 11, wherein: the active region includes a firstsemiconductor material having a first bandgap energy; a bulk material ofthe semiconductor structure includes a second semiconductor materialhaving a second bandgap energy that is greater than the first bandgapenergy, the bulk material connected to the active region; and thedielectric layer includes a dielectric material having a third bandgapenergy that is greater than the second bandgap energy.
 13. The method ofclaim 11, wherein the dielectric layer is configured to support anelectric field that draws charge carriers from a bulk material of thesemiconductor structure to the active region when the first voltage orthe second voltage is applied to the electrode.
 14. The method of claim11, wherein the first voltage reverse biases the semiconductorstructure, and wherein the second voltage forward biases thesemiconductor structure.
 15. The method of claim 11, wherein the activeregion is configured to accumulate charge carriers drawn from a bulkmaterial of the semiconductor structure in response to applying thefirst voltage.
 16. The method of claim 15, wherein the active region isconfigured to emit the electromagnetic radiation while the chargecarriers accumulated therein are depleted in response to applying thesecond voltage.
 17. A method of forming a light emitter, comprising:forming a semiconductor structure including an active region and a bulkmaterial having a first surface and a third surface opposite the firstsurface and connected to a fourth surface of the active region, whereinthe active region is configured to emit electromagnetic radiation, andwherein the bulk material is configured to supply charge carriers to theactive region; forming a first electrode including a first conductivecontact directly connected to the first surface of the bulk material,wherein the first electrode is configured to supply a currentcorresponding to the charge carriers that the bulk material supplies tothe active region; and forming a second electrode including a dielectriclayer and a second conductive contact connected to the dielectric layer,wherein the dielectric layer is adjacent to a second surface of theactive region opposite the fourth surface such that the secondconductive contact, the dielectric layer, and the semiconductorstructure collectively form a metal-oxide-semiconductor capacitor, andwherein the dielectric layer is configured to support an electric fieldwhen an electrical bias is applied between the first conductive contactand the second conductive contact.
 18. The method of claim 17, wherein:the active region includes a first semiconductor material having a firstbandgap energy; the bulk material includes a second semiconductormaterial having a second bandgap energy that is greater than the firstbandgap energy; and the dielectric layer includes a dielectric materialhaving a third bandgap energy that is greater than the second bandgapenergy.
 19. The method of claim 17, further comprising: forming a spacerdisposed between the active region and the dielectric layer, wherein thespacer is configured to reduce interfacial states between the activeregion and the dielectric layer.